1. Field of the Invention
The present invention relates to an image forming apparatus for a dry electrophotographic developing apparatus and the like, and in particular it elates to an image forming apparatus equipped with such a developing apparatus in which a toner and a carrier corresponding in amounts to their consumptions are replenished to a developer material supply path from a toner replenishment device and a carrier replenishment device thereby to maintain the mixing ratio by weight between the toner and the carrier constituting the developer material and the amount of the developer material held in the developer material supply path at constant levels, respectively, wherein a part of the developer material held in the developer material supply path is supplied to a photoreceptor through a developing roller while being stirred, so that a latent image formed on the photoreceptor is visualized by the toner contained in the developer material thus supplied, and at the same time, that part of the developer material to be held in the developer material supply path which exceeds a predetermined amount is discharged as a discharged developer material from a developer material discharge port and received in a discharged developer material receiving part.
2. Description of the Related Art
In a developing apparatus of an image forming apparatus applying an electrophotographic method, a method (trickle development) using a developer material composed of at least two components, a carrier and a toner, is mainstream. In the case of a developing apparatus using such a type of developer material, it is necessary to stir a carrier and a toner thereby to electrify the toner through stirring friction. However, a resin constituting the toner is fused to the carrier due to the heat of stirring friction, so that the carrier is gradually coated with the fused toner, finally reaching a state in which the carrier is contaminated by coatings. Thus, when the carrier comes to the state of contamination, it becomes impossible to sufficiently electrify the toner by the stirring friction, resulting in the formation of defective images. In order to avoid such defective images, conventionally, the entire amount of developer material has been replaced with a new one when the period of use of the developer material exceeds a prescribed period of time.
When the developer material is taken out of a container for such a replacement, there might arise a problem that the developer material is dispersed or scattered around to float in the surroundings and contaminate the surrounding environment. Accordingly, it is necessary to carry out the replacement of the developer material carefully, and hence replacing the entire developer material requires a lot of time. Thus, it has been proposed to replace the container storing the developer material on the whole in order to avoid such an annoying or troublesome replacement operation. However, by merely facilitating the replacement of the container without taking appropriate measures as to how to use the developer material, the amount of developer material to be wasted is not decreased at all. The developer material cannot be wasted or discarded as general garbage. Therefore, it is necessary to perform special processing on the developer material to be discarded. Thus, as the amount of wasted developer material increases, the cost of maintaining the developing apparatus increases, too.
As an invention with a possibility of solving the above-mentioned problem, there is a developing apparatus for an electrophotographic copier using a trickle development method as disclosed in Japanese Patent Publication No. 2-21591 (corresponding to U.S. Pat. No. 4,614,165). In this developing apparatus, a new carrier is replenished to the developing apparatus little by little in accordance with the replenishment of a toner, and a part of the surplus developer material is similarly discharged from the developing apparatus to a developer material collection tank little by little, whereby the developer material in the developing apparatus is continuously refreshed little by little. As a result, the deterioration speed of the electrification performance of the developer material used can be greatly slowed down, so that the usable life of the developer material can be extended to the same extent as the service life of the developing apparatus. In this developing apparatus, however, only the height of a weir installed in a discharge port is finally controlled so as to adjust the discharge of the deteriorated developer material, but the amount of the discharge is not fed back to the amount of supply of the developer material. Thus, it is impossible to perform the replenishment or discharge of the developer material at an amount corresponding to the amount of the discharge or replenishment thereof in an accurate manner. As a result, the amount of developer material in a development tank varies, making it impossible to carry out the precise control of keeping the concentration of the toner and the electrification performance of the developer material in the development tank in a good condition.
Thus, there have been made proposals for improved developing apparatuses such as, for example, those disclosed in Japanese Patent No. 2,986,001 (corresponding to U.S. Pat. No. 5,548,385) and in Japanese Patent No. 2,930,834 (corresponding to U.S. Pat. No. 5,592,270). In the developing apparatus disclosed in the Japanese Patent No. 2,986,001, a toner concentration sensor is arranged in a development tank, and a magnetic permeability sensor is arranged in a developer material collection tank. A control unit calculates the amount of developer material in the development tank from outputs of the toner concentration sensor and the magnetic permeability sensor, and performs control in such a manner that the amount of developer material in the development tank is made constant, thereby keeping the electrification performance thereof in a good condition. On the other hand, in the developing apparatus disclosed in Japanese Patent No. 2,930,834, a shutter, which can be opened and closed under the action of a solenoid, is arranged in a discharge port, and it is controlled to discharge a developer material at an amount corresponding to the amount of replenishment thereof. However, with the arrangements in the above examples as disclosed in Japanese Patent No. 2,986,001 and in Japanese Patent No. 2,930,834, the component parts employed are expensive and the control required thereof becomes complicated since the magnetic permeability sensor or the like is arranged in the developer material collection tank, or the shutter is arranged in the developer material discharge port, so that the sensor or shutter is controlled by a control circuit to keep the amount of developer material in the development tank at a constant level so as not to deteriorate the electrification performance of the developer material in the development tank. In addition, in cases where developing is performed in full color, it is necessary to install four sets of these elements in the developing apparatus, thus resulting in a substantial increase in the cost.
The present invention has been made to solve the above-mentioned problems, and has for its object to provide an image forming apparatus which is capable of keeping the weight ratio between a toner and a carrier in a developer material inside a development tank as well as the amount of the developer material at their prescribed constant values even with the use of simple component parts and easy control.
In order to solve the above-mentioned problems, the present invention resides in an image forming apparatus equipped with a developing apparatus in which a toner and a carrier constituting a developer material are replenished from a replenishment device to a developer material supply path, and in which an excess part of the amount of developer material to be held in the developer material supply path is discharged from a developer material discharge port as a discharged developer material and received in a discharged developer material receiving part. The developing apparatus, for the purpose of replenishing the carrier, includes: a discharged developer material weighing mechanism which receives the discharged developer material discharged from the developer material discharge port, and discharges the discharged developer material thus received into the discharged developer material receiving part each time the accumulated weight of the received discharged developer material reaches a prescribed weight; a sensor which detects that the discharged developer material weighing mechanism has discharged the discharged developer material into the discharged developer material receiving part; and a control unit which calculates an amount of discharge carrier corresponding to the detection of the sensor, and replenishes the carrier corresponding to the amount of discharged carrier thus calculated from the replenishment device into the developer material supply path.
With such a construction, the discharged developer material weighing mechanism receives the discharged developer material discharged from the developer material discharge port, and each time the accumulated weight of the received discharged developer material reaches a prescribed weight, the received discharged developer material is discharged into the discharged developer material receiving part. This discharge is detected by the sensor, and the control unit counts this detection and calculates an amount of carrier decreased, as a result of which the control unit drives the replenishment device to replenish the carrier. On the other hand, the consumption of the toner is detected by a toner concentration sensor, and the control unit replenishes the toner from the replenishment device. The mixing ratio by weight of the toner and the carrier, which together constitute the developer material, and the amount of developer material held in the developer material supply path is kept constant under such a control operation of the control unit.
In addition, in the present invention, the discharged developer material weighing mechanism includes: a rotation arm which is able to perform a seesaw movement about a rotation shaft within a prescribed angle range; a weight member which is mounted on one end of the rotation shaft; and a pocket which is mounted on the other end of the rotation arm and has a container shape for receiving the discharged developer material discharged from the developer material discharge port. The pocket is operable to rotate the rotation arm against the weight of the weight member and at the same time to discharge the discharged developer material received up to that time into the discharged developer material receiving part when the weight of the received discharged developer material exceeds a threshold. The pocket together with the rotation arm is returned to its original position under the action of the weight member after the discharge. Thus, the discharged developer material weighing mechanism is constituted by mechanical parts of simple structure, and hence achievement and handling thereof are easy.
Moreover, in the present invention, the discharged developer material weighing mechanism includes a lock mechanism which acts to lock the rotation arm against rotation thereof when a main electric power supply is turned off, and release the locking of the rotation arm when the main electric power supply is turned on. Thus, even if the image forming apparatus is inclined due to its movement or the like when the main electric power supply is turned off, the discharge of a large amount of developer material is prevented.
Further, in the present invention, the weight member is constructed such that a distance thereof from the rotation shaft is adjustable. Accordingly, it is possible to adjust the weight of the discharged developer material as necessary which can be measured at one time by the discharged developer material weighing mechanism.
Furthermore, in the present invention, the control unit calculates the accumulated amount of developer material discharged into the discharged developer material receiving part based on the number of detections of the sensor, and when a prescribed amount of accumulation is reached, the control unit displays an indication of that effect at a display device, or generates a warning sound. Thus, an operator is able to automatically learn the timing at which the discharged developer material receiving part should be replaced with an empty one without the arrangement of a complicated detection mechanism.
Still further, in the present invention, the developer material supply path comprises: a first developer material supply path section disposed adjacent to a developing roller for mixing and transporting the developer material along the developing roller; and a second developer material supply path disposed on the opposite side of the developing roller along the first developer material supply path section. The developer material supply path is constructed such that the developer material is fed from a transportation terminating end of the second developer material supply path section at a transportation starting end of the first developer material supply path section. The developer material is fed from a transportation terminating end of the first developer material supply path section to a transportation starting end of the second developer material supply path section at the transportation terminating end of the first developer material supply path section, and at the same time, a part of the developer material is discharged from the developer material discharge port as a discharged developer material. A bottom of the first developer material supply path section at the transportation terminating end thereof becomes gradually shallow toward a direction of transportation. With this arrangement, the chances of the developer material staying at corners or the like of the transportation terminating end of the first developer material supply path section without being recirculated are extremely reduced.
Additionally, in the present invention, a bottom of the second developer material supply path section is constructed such that it becomes gradually shallow toward the direction of transportation at the transportation terminating end of the second developer material supply path section, too, as at the transportation terminating end of the first developer material supply path section. Thus, the chances of the developer material staying at corners or the like of the transportation terminating ends of the first and second developer material supply path sections without being recirculated are extremely reduced.
Further, in the present invention, the image forming apparatus is constructed such that a first auger and a second auger both extending in the direction of transportation of the developer material are disposed in the first and second developer material supply path sections, respectively, and that the outer diameter of the first auger at the transportation terminating end of the first developer material supply path section decreases toward the direction of transportation so as to correspond to the bottom of the first developer material supply path section which becomes gradually shallow toward the direction of transportation.
Furthermore, in the present invention, the image forming apparatus is constructed such that a first auger and a second auger both extending in the direction of transportation of the developer material are disposed in the first and second developer material supply path sections, respectively, and that the outer diameters of the first and second augers at the transportation terminating ends of the first and second developer material supply path sections decrease toward the direction of transportation so as to correspond to the bottoms of the first and second developer material supply path sections which become gradually shallow toward the direction of transportation.